Bax/Bak are believed to initiate apoptosis by forming a pore in the mitochondrial outer membrane that allowscytochrome c to escape into the cytoplasm and activate the pro-apoptotic caspase cascade. The anti-apoptoticBcl-2 andBcl-xL proteins inhibit cytochrome c release through the mitochondrial pore and also inhibit activation of the cytoplasmic caspase cascade by cytochrome c.[8]
Dephosphorylated BAD forms a heterodimer withBcl-2 andBcl-xL, inactivating them and thus allowingBax/Bak-triggered apoptosis. When BAD is phosphorylated byAkt/protein kinase B (triggered by PIP3), it forms the BAD-(14-3-3) protein heterodimer. This leavesBcl-2 free to inhibitBax-triggered apoptosis.[9] BAD phosphorylation is thus anti-apoptotic, and BAD dephosphorylation (e.g., by Ca2+-stimulatedCalcineurin) is pro-apoptotic. The latter may be involved in neural diseases such as schizophrenia.[10]
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